The pavement marking industry has long desired transparent, solid microspheres or beads that would be useful as brighter and more durable retroreflective lens elements in pavement markings. The transparent microspheres now most widely used for pavement markings are made of certain glasses, which are amorphous vitreous materials. Generally these glasses are of the soda-lime-silicate type having a refractive index of only about 1.5, which limits their retroreflective brightness. Glass microspheres can be scratched or chipped by grit and dirt particles on the highway.